Generators and Transformers
Physics 106
1. Transformers
Concepts:
2. Generators
  NBA sin t : The emf produced by
coil of N turns and area A rotating in a
magnetic field B with an angular frequency
of ω.
I 1V1  I 2V2
Equations:
Transformer:
N V
V2  2 1
N1
1
Resonant frequency: f 0 
2 LC
Sample
Problem
Tesla: AC
Edison: DC
Transformer:
A transformer on a pole near a factory steps the voltage down from 3,600 V to 120 V.
The transformer is to deliver 1,000 kW to the factory at 90% efficiency. Find (a) the
power delivered to the primary, (b) the current in the primary, and (c) the current in the
secondary.
In a model ac generator, a 500-turn rectangular coil, 8.0 cm by 20 cm, rotates at 120
rev/min in a uniform magnetic field of 0.60 T.
a. What is the maximum emf induced in the coil?
b. What is the instantaneous value of the emf in the coil at t = (π/32)s? Assume that
the emf is zero at t = 0.
c. What is the smallest value of t for which the emf will have its maximum value?
Physics
Hero
Nikolai Tesla and his lightening machine.
The basic function of the electric generator is which of the following conversion processes?
Sample
Exam
Question
a. mechanical energy to electrical
b. electrical energy to mechanical
c. low voltage to high or vice versa
d. alternating current to direct
A transformer consists of a 500-turn primary coil and a 2 000-turn secondary coil. If the current in
the secondary is 3.00 A, what is the primary current?
Sample
Exam
Question
Don’t
Worry
About
a. 0.750 A
b. 1.33 A
c. 12.0 A
d. 48.0 A
The Chapter on AC. Just skim it, look at the pictures and scan the equations. Pay attention to the
forms of the equations: what is the same and what is different between the equations used for
AC circuits and those you have been using for DC circuits? For example, the equation for
AC Power still has the general form of Power  I 2 R except with AC, the power is an
2
R.
average and the current is a “root-mean-square”: Pav  I rms